Low-fat vs. low-carbs for weight loss — it doesn’t matter

A study1 from Stanford reported this week in “The Journal of the American Medical Association” is going to dismay many loud-speaking people on the low-carb bandwagon. Also, this study contradicts an ad I saw on TV today for “23 and me.” That ad says that weight loss schemes designed to match your genes work better.

In this project called DIETFITS, about 600 overweight and obese people were given either a “healthy” low-fat diet or low-carb diet and watched for a year. They were not instructed try to eat fewer overall calories, but they all did eat about 550 fewer calories per day. This observation means that when you can’t eat every kind of food you might want, you wind up eating less. So both groups lost between 5-6% of their baseline weight. This is the secret of all diets — eating special means it is going to be less appetizing. That is also the reason all diets fail — when you lose weight, you get hungry, especially for the stuff you’re not supposed to eat.

They also looked at some genetic patterns and insulin responses that seemed to make a difference to the response to different diets in prior studies. But they could not find any diet-gene type interactions. Weight and weight loss patterns must be somehow genetic, though, because in both groups, some people lost as much as 66 pounds and some gained as much as 22 pounds. We just don’t know which genes yet. It’s complicated.

The only statistically significant differences between the groups were that in the low-fat diet group, the low-density lipoprotein (LDL-bad) cholesterol was lower, and in the low-carb group, the high-density lipoprotein (HDL-good) cholesterol and triglycerides were higher. So maybe that’s a small vote in favor of the low-fat group since LDL probably beats HDL and triglycerides as heart risk factors.

They also instructed the low-carb group to eat less added sugar and refined flour, and the low-fat group to not eat trans fats, and everybody was instructed to eat more vegetables, less processed foods and eat at home as much as possible. That was the “healthy” part. So I guess we’ve already agreed to that much of the diet gospel.

I can hardly wait to see the outcry of letters to the editor on this one.